如何在 Python 3.5 中键入提示属性?

How can I type hint an attribute in Python 3.5?(如何在 Python 3.5 中键入提示属性?)

问题描述

我有一个类，我希望属性的初始值为 None:

I have a class where I want the initial value of an attribute to be None:

class SomeClass:
    def __init__(self):
        self.some_attribute = None

如何添加类型提示，以便 IDE 了解 some_attribute 通常属于 AnotherClass 类型?

How can I add type hinting, so that the IDE understands that some_attribute is usually of the type AnotherClass?

推荐答案

在 Python 3.5 中，你必须写

In Python 3.5, you have to write

self.some_attribute = None  # type: AnotherClass

从 Python 3.6 开始，为变量添加了新的类型提示语法(PEP 526):

Since Python 3.6, new type hinting syntax was added for variables (PEP 526):

self.some_attribute: AnotherClass = None

这可能会让每个类型检查系统都抱怨，因为 None 实际上不是 AnotherClass 的实例.相反，您可以使用 typing.Union[None, AnotherClass]，或简写:

This will probably make every type-checking system complain, because None is in fact not an instance of AnotherClass. Instead, you can use typing.Union[None, AnotherClass], or the shorthand:

from typing import Optional
...
self.some_attribute: Optional[AnotherClass] = None

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